CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY THE UNTVERSITY OF MICHIGAN VOL.30, NO. 4, PP. 131-162 December 31,1998 CARPOLESTES SZMPSONZ, NEW SPECIES (MAMMALIA, PROPRIMATES) FROM THE LATE PALEOCENE OF THE CLARKS FORK BASIN, WYOMING JONATHAN I. BLOCH AND PHnIP D. GINGERICH MUSEUM OF PALEONTOLOGY THE UNIVERSITY OF MICHIGAN ANN ARBOR CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY Philip D. Gingerich, Director This series of contributions from the Museum of Paleontology is a medium for publication of papers based chiefly on collections in the Museum. When the number of pages issued is sufficient to make a volume, a title page plus a table of contents will be sent to libraries on the Museum's mailing list. This will be sent to individuals on request. A list of the separate issues may also be obtained by request. Correspondence should be directed to the Publications Secretary, Museum of Paleontology, The University of Michigan, Ann Arbor, Michigan 48 109- 1079. VOLS. 2-29 Parts of volumes may be obtained if available. Price lists are available upon inquiry. Text and illustrations 01998 by the Museum of Paleontology, University of Michigan CARPOLESTES SZMPSONZ, NEW SPECIES (MAMMALIA, PROPRIMATES) FROM THE LATE PALEOCENE OF THE CLARKS FORK BASIN, WYOMING BY JONATHAN I. BLOCH AND PHILIP D. GINGERICH Abstract - Carpolestes is a small North American late Paleocene mammal with distinctively specialized premolar teeth. P3 is polycuspate with a distinct anteroexternal extension, and P4 is high-crowned, bladelike, and multicuspate. Carpolestes is now known from at least 180 specimens representing four mor- phologically and stratigraphically distinct species. Fossils from freshwater lime- stones of the Clarks Fork Basin include complete dentitions of a new species, Carpolestes simpsoni, from Clarkforkian faunal zones Cf-2 and earliest Cf-3. This is the youngest known species, and it differs from older species in having a more reduced dental formula of 3.0.3.312.1.1.3 with P3 absent. It differs in being smaller (ca. 100 g) and in having P3 and P4 of unique size and shape. New specimens show that the three teeth anterior to P2 are rooted in the premaxilla, meaning that Carpolestes retained three upper incisors (as has been reported for certain species of Elphidotarsius and Carpodaptes). I1 of Carpolestes resembles Carpodaptes in having a strong laterocone. The Carpolestes lineage decreased in size over time from the middle Tiffanian through the middle Clarkforkian land-mammal ages. Analysis of this evolution- ary time series shows the average base rate of change of tooth size (MI area) to have been about 0.002 standard deviations per generation. The temporal scaling slope is -0.52, which is close to expectation for random change and significantly different from expectation for either stasis or simple directional change. INTRODUCTION Carpolestidae are small, primate-like mammals that first appeared in the middle Paleocene and survived through the late Paleocene in North America. They are distinctive in having enlarged central incisors, a reduced anterior dentition (posterior to 11), and a plagiaulacoid structure of P4, with correlated specializations of P3-4 (Simpson, 1935; Szalay, 1972; Rose, 1975; Szalay and Delson, 1979). Twelve species are recognized in North America that are usually classified in three genera: Elphidotarsius, Carpodaptes, and Carpolestes (Simpson, 1935; Rose, 1975,1977; Holtzman, 1978; Krause, 1978; Gingerich, 1980; Fox, 1984,1993; Bloch and Gingerich, 1994). Szalay and Delson (1979) recognized only Elphidotarsius and Carpodaptes as valid genera. The three genera have been thought to form a morphologic and stratigraphic sequence indicating that they were repre- sentatives of a single rapidly-evolving clade (Rose, 1975, 1977). 132 J. I. BLOCH AND P. D. GINGERICH The oldest carpolestid, Elphidotarsius, first appeared in faunal zone To-3 of the Torrejonian land-mammal age, along with several other proprimates including the picrodontid Picrodus, the plesiadapid Pronothodectes, and the paromomyid Zgnacius (Archibald et al., 1987). The youngest of North American carpolestids, Carpolestes simpsoni (sp. nov.), is found in Clarkforkian faunal zones Cf-2 and the earliest part of Cf-3, with and just after the last occurrence of the largest known species of Plesiadapis, Plesiadapis cookei (Rose, 1981; Gingerich, 1980; Gingerich, 1983;Archibald et al., 1987). The only carpolestid from Asia is from the early Eocene, and no Paleocene proprimates are known from the Asian continent (Beard and Wang, 1995). Fossils representing the genus Carpolestes have more than doubled in number since the last revision of the family (Rose, 1975). These include many recovered from freshwater limestones of the middle Clarkforkian (Cf-2) faunal zone of the Clarks Fork Basin, Wyoming. The new material includes complete mandibles, two skulls, several fragmentary rostra, and some possibly-associ- ated postcrania. Such complete preservation is exceptional for small fossil mammals, which are usually represented by fragmentary jaws and isolated teeth. Several publications describing material from Paleocene-Eocene freshwater limestones of the Clarks Fork Basin have appeared in the past decade (Gingerich, 1987; Gunnel1 and Gingerich, 1987; Rose and Gingerich, 1987; Houde, 1988; Beard and Houde, 1989; Beard, 1989a, 1990a; Kay et al., 1990, 1992; Houde and Olson, 1992, Rose et al., 1993; MacPhee et al., 1995; Bloch et al., 1998). These fossils have had a significant impact on the study of birds, insectivores, and plesiadapiform proprimates of the Paleocene and early Eocene. Dental terminology follows that of VanValen (1966) and Szalay (1969) in general, and Gingerich (1976) for cusp and crest nomenclature used to describe the incisors. Dimensions of the teeth and mandible have been measured as illustrated in Figure 1 using calipers and a binocular microscope. INSTITUTIONAL ABBREVIATIONS UM - Museum of Paleontology, University of Michigan, Ann Arbor YPM-PU - Princeton University collection at Yale Peabody Museum, New Haven HISTORY OF STUDY Carpolestes ("fruit stealer") was first described by Simpson (1928), based on Carpolestes nigridens from Bear Creek Montana. Simpson (1929) named Carpolestes aquilae, also from Bear Creek, and Jepsen (1930) described Carpolestes dubius from Princeton Quarry, Wyoming Rose (1975) revised the family Carpolestidae, reviewing previous literature and including emended diagnoses for all known taxa. Rose placed Carpolestidae (Simpson, 1935) in the infraorder Plesiadapiforrnes (Simons, 1972), superfamily Plesiadapoidea (Trouessart, 1897), and order Pri- mates (Linnaeus, 1758). Rose (1975) recognized three genera and nine species of Carpolestidae. He confirmed the position of E. florencae (Gidley, 1923) and E. shotgunensis (Gazin, 1971) in Elphidotarsius (Gidley, 1923). He placed C. aulacodon (Matthew and Granger, 1921), C. hazelae (Simpson 1936), C. hobackensis (Dorr, 1952), C. cygneus (Russell, 1967), and new species C. jepseni in Carpodaptes (Matthew and Granger, 1921). He also confirmed the positions of Carpolestes dubius (Jepsen, 1930) and Carpolestes nigridens (Simpson, 1928) in Carpolestes (Simpson, 1928). Rose (1975) synonymized C. aquilae (Simpson, 1929) with C. nigridens in an emended diag- nosis of C. nigridens, noting that distinguishing features cited by Simpson (1935) were typical of intraspecific variation while no characters consistently separated the two species. Rose (1975) followed Van Valen (1969) in removing European Saxonella from Carpolestidae but, instead of placing it in Plesiadapidae, as Van Valen had, suggested putting it in its own family Saxonellidae. Rose (1975) described the first known upper teeth of Elphidotarsius, and the first lower incisors of Elphidotarsius and Carpolestes. He inferred a dental formula of 2?. 1?.3?.3/2.1.2-3.3 for CARPOLESTES SIMPSONI FROM WYOMING FIG. 1 - Measurements taken on teeth and mandibles of Carpolestes, following, in part, Rose (1975: 4). A, 12-M3 in occlusal view; B, 11 in occlusal and lateral views; C, 11-M3in occlusal view; and D, 11-MIand part of dentary in lateral view. Lengths (L) are maximum anteroposterior crown dimensions, as shown. Widths (W) are maximum crown dimensions measured perpendicular to length. Height (H) is measured from the base of the enamel-dentin boundary to the tip of the crown. Mandibular depth (MD) is measured beneath the anterior root of MI. Measurements are summarized in Table 1 and listed individually in Appendix tables A1-A4. Carpolestidae, with PI absent and P2 reduced or lost in Carpodaptes and Carpolestes. Rose (1975) pointed out that the three carpolestid genera are restricted temporally, with Elphidotarsius in the Torrejonian, Carpodaptes in the Tiffanian, and Carpolestes in the Clarkforkian. Rose further considered that these genera formed a morphologic and stratigraphic sequence indicating that they were representatives of a single generic lineage. Rose cited morphological similarities between plesiadapids and carpolestids as an indication that the two families are closely related through a common ancestor that was possibly similar to Pronothodectes. Rose (1977) emphasized that Carpolestidae are useful for determining the sequence and corre- lation of North American Paleocene faunas because they are "rapidly evolving, morphologically distinctive, common and widespread, and found in all major lithofacies" (Rose, 1977: 536). Rose noted that individual taxa were of short duration and could be used for estimation of the age of vertebrate